At 5'6" tall,
James Polk was the shortest
President of the United States ever. Due to his diminuative stature, he could walk into the room at
White House parties, and no one would notice.
Polk's wife asked the Marine Corps band to find a song to play when Polk entered the room, so that her husband could get the respect he was due. The bandleader searched for songs, and settled on a little-known Scottish march entitled 'Hail to the Chief'.
The song worked so well, it became tradition for the next 31 presidents.
Source: A White House tour guide, as recorded by the crew of National Public Radio's All Things Considered